[PATCH] likely cleanup: remove unlikely for kfree(NULL)

On my system, it shows about 84K misses and 67K hits. So there are more kfree(NULL) than people
realize.

I know some people won't like it, but I think it's not worth the confusion and maintenance burden,
so I'm giving it a shot. :-)

Signed-off-by: Hua Zhong <hzhong@gmail.com>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
diff --git a/mm/slab.c b/mm/slab.c
index e6ef9bd..0fbc854 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3380,7 +3380,7 @@ void kfree(const void *objp)
  	struct kmem_cache *c;
  	unsigned long flags;

-	if (unlikely(!objp))
+	if (!objp)
  		return;
  	local_irq_save(flags);
  	kfree_debugcheck(objp);